Method for allocating ack/nack resource in wireless communication system and apparatus therefor

ABSTRACT

The present invention relates to a method and apparatus for feeding back acknowledgement/negative-ACK (ACK/NACK) by a receiving device in a wireless communication system. Specifically, the method comprises the steps of: receiving data from a transmitting device; and feeding back ACK/NACK for data to the transmitting device, wherein the size of resource for ACK/NACK is determined on the basis of a distance between the transmitting device and the receiving device. The receiving device is capable of communicating with at least one of another transmitting device, a transmitting device related to an autonomous driving vehicle, a base station or a network.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system, andmore particularly, to a method of allocating anacknowledgement/negative-acknowledgement (ACK/NACK) resource andapparatus therefor.

BACKGROUND ART

A 3rd generation partnership project long term evolution (3GPP LTE)(hereinafter, referred to as ‘LTE’) communication system which is anexample of a wireless communication system to which the presentinvention can be applied will be described in brief.

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS) which is an exampleof a wireless communication system. The E-UMTS is an evolved version ofthe conventional UMTS, and its basic standardization is in progressunder the 3rd Generation Partnership Project (3GPP). The E-UMTS may bereferred to as a Long Term Evolution (LTE) system. Details of thetechnical specifications of the UMTS and E-UMTS may be understood withreference to Release 7 and Release 8 of “3rd Generation PartnershipProject; Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), basestations (eNode B; eNB), and an Access Gateway (AG) which is located atan end of a network (E-UTRAN) and connected to an external network. Thebase stations may simultaneously transmit multiple data streams for abroadcast service, a multicast service and/or a unicast service.

One or more cells exist for one base station. One cell is set to one ofbandwidths of 1.44, 3, 5, 10, 15 and 20 MHz to provide a downlink oruplink transport service to several user equipments. Different cells maybe set to provide different bandwidths. Also, one base station controlsdata transmission and reception for a plurality of user equipments. Thebase station transmits downlink (DL) scheduling information of downlinkdata to the corresponding user equipment to notify the correspondinguser equipment of time and frequency domains to which data will betransmitted and information related to encoding, data size, and hybridautomatic repeat and request (HARQ). Also, the base station transmitsuplink (UL) scheduling information of uplink data to the correspondinguser equipment to notify the corresponding user equipment of time andfrequency domains that can be used by the corresponding user equipment,and information related to encoding, data size, and HARQ. An interfacefor transmitting user traffic or control traffic may be used between thebase stations. A Core Network (CN) may include the AG and a network nodeor the like for user registration of the user equipment. The AG managesmobility of the user equipment on a Tracking Area (TA) basis, whereinone TA includes a plurality of cells.

Although the wireless communication technology developed based on WCDMAhas been evolved into LTE, request and expectation of users andproviders have continued to increase. Also, since another wirelessaccess technology is being continuously developed, new evolution of thewireless communication technology will be required for competitivenessin the future. In this respect, reduction of cost per bit, increase ofavailable service, use of adaptable frequency band, simple structure andopen type interface, proper power consumption of the user equipment,etc. are required.

DISCLOSURE Technical Problem

Based on the above discussion, the present disclosure describes a methodof allocating an ACK/NACK resource in a wireless communication systemand apparatus therefor.

Technical tasks obtainable from the present invention are non-limited bythe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Technical Solution

In an aspect of the present disclosure, provided herein is a method offeeding back acknowledgement/negative-acknowledgement (ACK/NACK) by areceiving device in a wireless communication system. The method mayinclude: receiving data from a transmitting device; and feeding backACK/NACK for the data to the transmitting device. In this case, the sizeof an ACK/NACK resource may be determined based on a distance betweenthe transmitting device and the receiving device.

The ACK/NACK resource size may be determined as a resource sizeassociated with a specific range corresponding to a distance valuedepending on reference signal received power (RSRP) or locationinformation based on a predetermined range for the ACK/NACK resourcesize. In addition, information on the predetermined range and theACK/NACK resource size mapped to the predetermined range may beindicated through radio resource control (RRC) signaling.

The method may further include transmitting a demodulation referencesignal (DMRS) associated with the ACK/NACK to the transmitting device.In this case, a DMRS sequence may be determined based on the ACK/NACKresource size.

An ACK/NACK sequence may be determined based on the ACK/NACK resourcesize.

Only when the ACK/NACK resource is selected from a resource poolconfigured for a power-limited receiving device, the ACK/NACK resourcesize may be determined based on the distance between the transmittingdevice and the receiving device.

Only when it is indicated through higher layer signal or a controlchannel that an ACK/NACK size is determined based on the distancebetween the transmitting device and the receiving device, the ACK/NACKresource size may be determined based on the distance between thetransmitting device and the receiving device.

The ACK/NACK resource size may be indicated by the transmitting devicebased on the distance between the transmitting device and the receivingdevice.

In another aspect of the present disclosure, provided herein is a methodof receiving ACK/NACK by a transmitting device in a wirelesscommunication system. The method may include: transmitting data to areceiving device; and receiving ACK/NACK feedback for the data from thereceiving device. In this case, the size of an ACK/NACK resource may bedetermined based on a distance between the transmitting device and thereceiving device.

In a further aspect of the present disclosure, provided herein is areceiving device for feeding back ACK/NACK in a wireless communicationsystem. The receiving device may include a radio frequency unit and aprocessor. The processor may be configured to receive data from atransmitting device and feed back ACK/NACK for the data to thetransmitting device. In this case, the size of an ACK/NACK resource maybe determined based on a distance between the transmitting device andthe receiving device.

Advantageous Effects

According to the present disclosure, an ACK/NACK resource can beefficiently allocated in a wireless communication system.

Effects obtainable from the present invention are non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 schematically illustrates an E-UMTS network structure as anexample of a wireless communication system.

FIG. 2 illustrates control plane and user plane structures of a radiointerface protocol between a UE and an E-UTRAN on the basis of the 3GPPwireless access network standard.

FIG. 3 illustrates physical channels used in a 3GPP system and a generalsignal transmission method using the same.

FIG. 4 illustrates a radio frame structure used in LTE.

FIG. 5 illustrates a resource grid for a downlink slot.

FIG. 6 illustrates a structure of a downlink radio frame used in an LTEsystem.

FIG. 7 illustrates a structure of an uplink radio frame used in an LTEsystem.

FIG. 8 is a reference diagram to describe D2D (UE-to-UE) communication.

FIG. 9 is a reference diagram to describe a V2V scenario.

FIG. 10 and FIG. 11 are reference diagrams to describe a resource poolon a D2D scenario.

FIG. 12 shows a base station and a user equipment applicable to oneembodiment of the present invention.

BEST MODE

The following technology may be used for various wireless accesstechnologies such as CDMA (code division multiple access), FDMA(frequency division multiple access), TDMA (time division multipleaccess), OFDMA (orthogonal frequency division multiple access), andSC-FDMA (single carrier frequency division multiple access). The CDMAmay be implemented by the radio technology such as UTRA (universalterrestrial radio access) or CDMA2000. The TDMA may be implemented bythe radio technology such as global system for mobile communications(GSM)/general packet radio service (GPRS)/enhanced data rates for GSMevolution (EDGE). The OFDMA may be implemented by the radio technologysuch as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, andevolved UTRA (E-UTRA). The UTRA is a part of a universal mobiletelecommunications system (UMTS). A 3rd generation partnership projectlong term evolution (3GPP LTE) is a part of an evolved UMTS (E-UMTS)that uses E-UTRA and adopts OFDMA in a downlink and SC-FDMA in anuplink. LTE-advanced (LTE-A) is an evolved version of the 3GPP LTE.

For clarification of the description, although the following embodimentswill be described based on the 3GPP LTE/LTE-A, it is to be understoodthat the technical spirits of the present invention are not limited tothe 3GPP LTE/LTE-A. Also, specific terminologies hereinafter used in theembodiments of the present invention are provided to assistunderstanding of the present invention, and various modifications may bemade in the specific terminologies within the range that they do notdepart from technical spirits of the present invention.

FIG. 2 is a diagram illustrating structures of a control plane and auser plane of a radio interface protocol between a user equipment andE-UTRAN based on the 3GPP radio access network standard. The controlplane means a passageway where control messages are transmitted, whereinthe control messages are used by the user equipment and the network tomanage call. The user plane means a passageway where data generated inan application layer, for example, voice data or Internet packet dataare transmitted.

A physical layer as the first layer provides an information transferservice to an upper layer using a physical channel. The physical layeris connected to a medium access control (MAC) layer via a transportchannel, wherein the medium access control layer is located above thephysical layer. Data are transferred between the medium access controllayer and the physical layer via the transport channel Data aretransferred between one physical layer of a transmitting side and theother physical layer of a receiving side via the physical channel. Thephysical channel uses time and frequency as radio resources. In moredetail, the physical channel is modulated in accordance with anorthogonal frequency division multiple access (OFDMA) scheme in adownlink and is modulated in accordance with a single carrier frequencydivision multiple access (SC-FDMA) scheme in an uplink.

A medium access control (MAC) layer of the second layer provides aservice to a radio link control (RLC) layer above the MAC layer via alogical channel. The RLC layer of the second layer supports reliabledata transmission. The RLC layer may be implemented as a functionalblock inside the MAC layer. In order to effectively transmit data usingIP packets such as IPv4 or IPv6 within a radio interface having a narrowbandwidth, a packet data convergence protocol (PDCP) layer of the secondlayer performs header compression to reduce the size of unnecessarycontrol information.

A radio resource control (RRC) layer located on the lowest part of thethird layer is defined in the control plane only. The RRC layer isassociated with configuration, re-configuration and release of radiobearers (‘RBs’) to be in charge of controlling the logical, transportand physical channels. In this case, the RB means a service provided bythe second layer for the data transfer between the user equipment andthe network. To this end, the RRC layers of the user equipment and thenetwork exchange RRC message with each other. If the RRC layer of theuser equipment is RRC connected with the RRC layer of the network, theuser equipment is in an RRC connected mode. If not so, the userequipment is in an RRC idle mode. A non-access stratum (NAS) layerlocated above the RRC layer performs functions such as sessionmanagement and mobility management.

One cell constituting a base station eNB is set to one of bandwidths of1.4, 3.5, 5, 10, 15, and 20 MHz and provides a downlink or uplinktransmission service to several user equipments. At this time, differentcells may be set to provide different bandwidths.

As downlink transport channels carrying data from the network to theuser equipment, there are provided a broadcast channel (BCH) carryingsystem information, a paging channel (PCH) carrying paging message, anda downlink shared channel (SCH) carrying user traffic or controlmessages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted via the downlink SCH or anadditional downlink multicast channel (MCH). Meanwhile, as uplinktransport channels carrying data from the user equipment to the network,there are provided a random access channel (RACH) carrying an initialcontrol message and an uplink shared channel (UL-SCH) carrying usertraffic or control message. As logical channels located above thetransport channels and mapped with the transport channels, there areprovided a broadcast control channel (BCCH), a paging control channel(PCCH), a common control channel (CCCH), a multicast control channel(MCCH), and a multicast traffic channel (MTCH).

FIG. 3 is a diagram illustrating physical channels used in a 3GPP LTEsystem and a general method for transmitting a signal using the physicalchannels.

The user equipment performs initial cell search such as synchronizingwith the base station when it newly enters a cell or the power is turnedon at step S301. To this end, the user equipment synchronizes with thebase station by receiving a primary synchronization channel (P-SCH) anda secondary synchronization channel (S-SCH) from the base station, andacquires information such as cell ID, etc. Afterwards, the userequipment may acquire broadcast information within the cell by receivinga physical broadcast channel (PBCH) from the base station. Meanwhile,the user equipment may identify a downlink channel status by receiving adownlink reference signal (DL RS) at the initial cell search step.

The user equipment which has finished the initial cell search mayacquire more detailed system information by receiving a physicaldownlink shared channel (PDSCH) in accordance with a physical downlinkcontrol channel (PDCCH) and information carried in the PDCCH at stepS302.

Afterwards, the user equipment may perform a random access procedure(RACH) such as steps S303 to S306 to complete access to the basestation. To this end, the user equipment may transmit a preamble througha physical random access channel (PRACH) (S303) and may receive aresponse message to the preamble through the PDCCH and the PDSCHcorresponding to the PDCCH (S304). In case of a contention based RACH,the user equipment may perform a contention resolution procedure such astransmission (S305) of additional physical random access channel andreception (S306) of the physical downlink control channel and thephysical downlink shared channel corresponding to the physical downlinkcontrol channel.

The user equipment which has performed the aforementioned steps mayreceive the physical downlink control channel (PDCCH)/physical downlinkshared channel (PDSCH) (S307) and transmit a physical uplink sharedchannel (PUSCH) and a physical uplink control channel (PUCCH) (S308), asa general procedure of transmitting uplink/downlink signals. Controlinformation transmitted from the user equipment to the base station willbe referred to as uplink control information (UCI). The UCI includesHARQ ACK/NACK (Hybrid Automatic Repeat and reQuestAcknowledgement/Negative-ACK), SR (Scheduling Request), CSI (ChannelState Information), etc. In this specification, the HARQ ACK/NACK willbe referred to as HARQ-ACK or ACK/NACK (A/N). The HARQ-ACK includes atleast one of positive ACK (simply, referred to as ACK), negative ACK(NACK), DTX and NACK/DTX. The CSI includes CQI (Channel QualityIndicator), PMI (Precoding Matrix Indicator), RI (Rank Indication), etc.Although the UCI is generally transmitted through the PUCCH, it may betransmitted through the PUSCH if control information and traffic datashould be transmitted at the same time. Also, the user equipment maynon-periodically transmit the UCI through the PUSCH in accordance withrequest/command of the network.

FIG. 4 is a diagram illustrating a structure of a radio frame used in anLTE system.

Referring to FIG. 4, in a cellular OFDM radio packet communicationsystem, uplink/downlink data packet transmission is performed in a unitof subframe, wherein one subframe is defined by a given time intervalthat includes a plurality of OFDM symbols. The 3GPP LTE standardsupports a type 1 radio frame structure applicable to frequency divisionduplex (FDD) and a type 2 radio frame structure applicable to timedivision duplex (TDD).

FIG. 4(a) is a diagram illustrating a structure of a type 1 radio frame.The downlink radio frame includes 10 subframes, each of which includestwo slots in a time domain. A time required to transmit one subframewill be referred to as a transmission time interval (TTI). For example,one subframe may have a length of 1 ms, and one slot may have a lengthof 0.5 ms. One slot includes a plurality of OFDM symbols in a timedomain and a plurality of resource blocks (RB) in a frequency domain.Since the 3GPP LTE system uses OFDM in a downlink, OFDM symbolsrepresent one symbol interval. The OFDM symbol may be referred to asSC-FDMA symbol or symbol interval. The resource block (RB) as a resourceallocation unit may include a plurality of continuous subcarriers in oneslot.

The number of OFDM symbols included in one slot may be varied dependingon configuration of a cyclic prefix (CP). Examples of the CP include anextended CP and a normal CP. For example, if the OFDM symbols areconfigured by the normal CP, the number of OFDM symbols included in oneslot may be 7. If the OFDM symbols are configured by the extended CP,since the length of one OFDM symbol is increased, the number of OFDMsymbols included in one slot is smaller than that of OFDM symbols incase of the normal CP. For example, in case of the extended CP, thenumber of OFDM symbols included in one slot may be 6. If a channel stateis unstable like the case where the user equipment moves at high speed,the extended CP may be used to reduce inter-symbol interference.

If the normal CP is used, since one slot includes seven OFDM symbols,one subframe includes 14 OFDM symbols. At this time, first maximum threeOFDM symbols of each subframe may be allocated to a physical downlinkcontrol channel (PDCCH), and the other 01-DM symbols may be allocated toa physical downlink shared channel (PDSCH).

FIG. 4(b) is a diagram illustrating a structure of a type 2 radio frame.The type 2 radio frame includes two half frames, each of which includesfour general subframes, which include two slots, and a special subframewhich includes a downlink pilot time slot (DwPTS), a guard period (GP),and an uplink pilot time slot (UpPTS).

In the special subframe, the DwPTS is used for initial cell search,synchronization or channel estimation at the user equipment. The UpPTSis used for channel estimation at the base station and uplinktransmission synchronization of the user equipment. In other words, theDwPTS is used for downlink transmission, whereas the UpPTS is used foruplink transmission. Especially, the UpPTS is used for PRACH preamble orSRS transmission. Also, the guard period is to remove interferenceoccurring in the uplink due to multipath delay of downlink signalsbetween the uplink and the downlink.

Configuration of the special subframe is defined in the current 3GPPstandard document as illustrated in Table 1 below. Table 1 illustratesthe DwPTS and the UpPTS in case of Ts=1/(15000×2048), and the otherregion is configured for the guard period.

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink Special UpPTS UpPTS subframe Normal cyclic Extended cyclicNormal cyclic Extended cyclic configuration DwPTS prefix in uplinkprefix in uplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s)2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 119760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — —9 13168 · T_(s) — — —

In the meantime, the structure of the type 2 radio frame, that is,uplink/downlink configuration (UL/DL configuration) in the TDD system isas illustrated in Table 2 below.

TABLE 2 Downlink- Uplink- to-Uplink downlink Switch- config- pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 msD S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D DD D 6 5 ms D S U U U D S U U D

In the above Table 2, D means the downlink subframe, U means the uplinksubframe, and S means the special subframe. Also, Table 2 alsoillustrates a downlink-uplink switching period in the uplink/downlinksubframe configuration of each system.

The structure of the aforementioned radio frame is only exemplary, andvarious modifications may be made in the number of subframes included inthe radio frame, the number of slots included in the subframe, or thenumber of symbols included in the slot.

FIG. 5 illustrates a resource grid for a downlink slot.

Referring to FIG. 5, a DL slot includes N_symb{circumflex over ( )}DLOFDM symbols in a time domain and N_RB{circumflex over ( )}DL resourceblocks in a frequency domain. Since each of the resource blocks includesN_SC{circumflex over ( )}RB subcarriers, the DL slot includesN_RB{circumflex over ( )}DL×N_SC{circumflex over ( )}RB subcarriers inthe frequency domain. Although FIG. 5 shows an example in which the DLslot includes 7 OFDM symbols and the resource block includes 12subcarriers, the present invention is not limited thereto. For instance,the number of OFDM symbols included in the DL slot can vary depending toa length of a cyclic prefix (CP).

Each element on a resource grid is referred to as a resource element(RE) and a single resource element is indicated by one OFDM symbol indexand one subcarrier index. A single RB is configured withN_symb{circumflex over ( )}DL×N_SC{circumflex over ( )}RB resourceelements. The number (N_RB{circumflex over ( )}DL) of resource blocksincluded in the DL slot depends on a DL transmission bandwidthconfigured in a cell.

FIG. 6 illustrates a structure of a downlink radio frame.

Referring to FIG. 6, up to 3 (or 4) OFDM symbols located at a head partof a first slot of a subframe correspond to a control region to which acontrol channel is assigned. And, the rest of OFDM symbols correspond toa data region to which PDSCH (physical downlink shared channel) isassigned. For example, DL control channels used in the LTE system mayinclude a PCFICH (physical control format indicator channel), a PDCCH(physical downlink control channel), a PHICH (physical hybrid ARQindicator channel) and the like. The PCFICH is transmitted on a firstOFDM symbol of a subframe and carries information on the number of OFDMsymbols in the subframe used for control channel transmission. The PHICHcarries an HARQ ACK/NACK (hybrid automatic repeat requestacknowledgment/negative-acknowledgment) signal in response to ULtransmission.

Control information transmitted on the PDCCH is called DCI (downlinkcontrol information). The DCI includes resource allocation informationand other control information for a user equipment or a user equipmentgroup. For instance, the DCI may include UL/DL scheduling information,UL transmission (Tx) power control command and the like.

The PDCCH carries transmission format and resource allocationinformation of a DL-SCH (downlink shared channel), transmission formatand resource allocation information of a UL-SCH (uplink shared channel),paging information on a PCH (paging channel), system information on aDL-SCH, resource allocation information of a higher-layer controlmessage such as a random access response transmitted on a PDSCH, a Txpower control command set for individual user equipments in a userequipment group, a Tx power control command, activation indicationinformation of a VoIP (voice over IP) and the like. A plurality ofPDCCHs may be transmitted in a control region. A user equipment canmonitor a plurality of PDCCHs. The PDCCH is transmitted on aggregationof one or more consecutive CCEs (control channel elements). In thiscase, the CCE is a logical assignment unit used in providing the PDCCHwith a coding rate based on a radio channel state. The CCE correspondsto a plurality of REGs (resource element groups). The PDCCH format andthe number of PDCCH bits are determined depending on the number of CCEs.A base station determines the PDCCH format in accordance with DCI to betransmitted to a user equipment and attaches CRC (cyclic redundancycheck) to control information. The CRC is masked with an identifier(e.g., RNTI (radio network temporary identifier)) in accordance with anowner or a purpose of use. For instance, if a PDCCH is provided for aspecific user equipment, CRC may be masked with an identifier (e.g.,C-RNTI (cell-RNTI)) of the corresponding user equipment. If a PDCCH isprovided for a paging message, CRC may be masked with a pagingidentifier (e.g., P-RNTI (paging-RNTI)). If a PDCCH is provided forsystem information (particularly, SIC (system information block)), CRCmay be masked with an SI-RNTI (system information-RNTI). In addition, ifa PDCCH is provided for a random access response, CRC may be masked withan RA-RNTI (random access-RNTI).

FIG. 7 illustrates a structure of an uplink subframe used in an LTEsystem.

Referring to FIG. 7, an uplink subframe includes a plurality (e.g., 2slots) of slots. Each of the slots may include a different number ofSC-FDMA symbols depending on a length of CP. The UL subframe may bedivided into a data region and a control region in the frequency domain.The data region includes a PUSCH and is used to transmit such a datasignal as audio and the like. The control region includes a PUCCH and isused to transmit UCI (uplink control information). The PUCCH includes anRB pair located at both ends of the data region on a frequency axis andis hopped on a slot boundary.

The PUCCH can be used to transmit the following control information.

-   -   SR (scheduling request): This is information used to request a        UL-SCH resource and is transmitted using an OOK (on-off keying)        scheme.    -   HARQ ACK/NACK: This is a response signal in response to a DL        data packet on a PDSCH and indicates whether the DL data packet        has been successfully received. 1-bit ACK/NACK is transmitted as        a response to a single downlink codeword and 2-bit ACK/NACK is        transmitted as a response to two downlink codewords.    -   CSI (channel state information): This is feedback information on        a downlink channel. The CSI includes a channel quality indicator        (CQI). MIMO (multiple input multiple output) related feedback        information includes a rank indicator (RI), a precoding matrix        indicator (PMI), a precoding type indicator (PTI) and the like.        20-bit is used in each subframe.

The amount of control information (UCI) that a user equipment cantransmit in a subframe depends on the number of SC-FDMA symbolsavailable for transmission of the control information. The SC-FDMAsymbols available for the transmission of the control informationcorrespond to the rest of SC-FDMA symbols except SC-FDMA symbols usedfor transmitting a reference signal in the subframe. In case of asubframe in which a sounding reference signal (SRS) is configured, thelast SC-FDMA symbol of the subframe is excluded from the SC-FDMA symbolsavailable for the transmission of the control information. The referencesignal is used for coherent detection of a PUCCH.

Hereinafter, D2D (UE-to-UE) communication will be described.

A D2D communication scheme can be mainly classified as a schemesupported by a network/coordination station (e.g., base station) and ascheme not supported by the network/coordination station.

Referring to FIG. 8, FIG. 8 (a) illustrates a scheme in which thenetwork/coordination station intervenes in transmission and reception ofcontrol signals (e.g., grant message), HARQ, channel state information,etc. and user equipments that perform D2D communication transmit andreceive data only. On the other hand, FIG. 8 (b) illustrates a scheme inwhich the network provides minimum information (e.g., D2D connectioninformation available in a corresponding cell) only but the userequipments that perform D2D communication establish links to transmitand receive data.

FIG. 9 is a diagram illustrating a V2X (vehicle to everything)communication environment.

If a vehicle accident occurs, many lives are lost, and serious propertydamage is caused. Thus, the demand for a technology capable of securingsafety of pedestrians as well as safety of people in a vehicle has beenincreased. In addition, a technology based on hardware and softwarededicated to the vehicle has been grafted onto the vehicle.

Recently, the LTE-based V2X (vehicle-to-everything) communicationtechnology, which has been evolved from 3GPP, reflects the tendency inwhich the information technology (IT) is grafted onto the vehicle. Aconnectivity function is applied to some kinds of vehicles, and effortsare continuously made to research and develop vehicle-to-vehicle (V2V)communication, vehicle-to-infrastructure (V2I) communication,vehicle-to-pedestrian (V2P) communication, and vehicle-to-network (V2N)communication with the evolution of communication functions.

According to V2X communication, a vehicle consistently broadcastsinformation on its own locations, speeds, directions, etc. Afterreceiving the broadcasted information, a nearby vehicle utilizes theinformation for accident prevention by recognizing movements of otheradjacent vehicles.

That is, in a similar manner that an individual person carries a userequipment such as a smartphone, a smartwatch or the like, a specifictype of user equipment (UE) can be installed in each vehicle. Here, a UEinstalled in a vehicle means a device that actually receivescommunication services from a communication network. For example, the UEinstalled in the vehicle can be accessed to an eNB in E-UTRAN andprovided with communication services.

However, there are various items that should be considered for a processfor implementing V2X communication in a vehicle. This is becauseastronomical costs are required for the installation of traffic safetyfacilities such as a V2X base station and the like. That is, to supportV2X communication on all roads where the vehicle can move, it isnecessary to install hundreds or thousands of V2X base stations or more.Moreover, since each network node accesses the Internet or a centralizedcontrol server using a wired network basically for stable communicationwith a server, installation and maintenance costs for the wired networkare also high.

Hereinafter, resource allocation for performing V2X communication in thepresent invention is described. Although the present invention isdescribed by being limited to a V2X scenario for clarity of thedescription, the present invention is applicable to other communicationsystems such as Device-to-Device (D2D) communication.

FIG. 10 is a reference diagram to describe UE-to-UE directcommunication. When a UE performs communication with another UE using adirect wireless channel, as shown in FIG. 10, the present inventionproposes a method of determining a resource to use for communication.This can be named UE-to-UE direct signal transmission/reception orDevice-to-Device (D2D) communication, and further named a sidelink to bedistinguished from Downlink (DL) and Uplink (UL) of the existingcellular communication. Furthermore, communication among multipledevices may be named Vehicle-to-Vehicle (V2V) communication inassociation with vehicles. Hence, although a UE means a user's UE (orcar), if a network equipment such as an eNB transmits/receives a signalaccording to a UE-to-UE communication methodology, the network equipmentcan be regarded as a sort of UE to which the present invention isapplicable. Moreover, an eNB can receive a D2D signal transmitted by aUE. Furthermore, a signal transmitting/receiving method of a UE designedfor D2D transmission is applicable to an operation for a UE to transmitdata to an eNB.

In the following description, UE1 may operate in a manner of selecting aresource unit corresponding to a specific resource from a resource poolmeaning a set of a series of resources and transmitting a D2D signalusing the corresponding resource unit. UE2 that is an Rx UE may receivea configuration of a resource pool for the UE1 to transmit a D2D signaland detect a signal of the UE1 within the corresponding resource pool.Here, if the UE1 is in a connection range of a base station, the UE1 canbe informed of the resource pool by the base station. If the UE1 is outof the connection range of the base station, the UE1 may be informed ofthe resource pool by another UE or the resource pool may be determinedas a previously determined resource. Generally, a resource pool isconfigured in a plurality of resource units. Each UE may select a singleor a plurality of resource units and use the selected resource unit(s)for D2D signal transmission of its own.

FIG. 11 shows one example of a configuration of resource unit. FIG. 11illustrates a case that total NF*NT resource units are defined in amanner of dividing a full frequency resource into NF units and dividinga full time resource into NT units. In FIG. 11, a corresponding resourcepool is repeated every NT subframes. Typically, as shown in FIG. 11, asingle resource unit may appear in a manner of being repeatedperiodically. Or, an index of a physical resource unit, to which onelogical resource unit is mapped to obtain a diversity effect in a timeor frequency dimension, may change in a predetermined pattern accordingto a time. In such a resource unit structure, a resource pool may mean aset of resource units usable for a transmission by a UE intending totransmit a D2D signal.

Furthermore, a resource pool can be subdivided into various types. Firstof all, a resource pool can be divided according to a content of atransmitted D2D signal in each resource pool. For example, a content ofa D2D signal can be classified as follows. And, a separate resource poolmay be configured for each content.

-   -   Scheduling Assignment (SA) (or sidelink control channel): Signal        including information such as a location of a resource used for        transmission of a following D2D data channel by each        transmitting (Tx) UE, a Modulation and Coding Scheme (MCS)        required for demodulation of a data channel, an MIMO        transmission methodology and the like. Such an SA signal can be        transmitted on the same resource unit by being multiplexed with        D2D data. In this case, an SA resource pool may mean a resource        pool configured with a resource on which an SA is transmitted by        being multiplexed with D2D data.    -   D2D data channel (sidelink shared channel): A resource pool        configured with a resource used in transmitting user data by a        Tx UE using a resource designated through SA. If a transmission        on the same resource unit by being multiplexed with D2D data is        possible, only a D2D data channel of a type except SA        information is transmitted in a resource pool for the D2D data        channel. So to speak, a resource element used in transmitting SA        information on an individual resource unit within an SA resource        pool is still used to transmit D2D data in a D2D data channel        resource pool.    -   Discovery message (or sidelink discovery channel): A resource        pool for a message through which a Tx UE enables an adjacent UE        to discover the Tx UE itself by transmitting information such as        an ID of the Tx UE and the like.    -   Synchronization signal/channel (or, sidelink synchronization        signal, sidelink broadcast channel): A resource pool for a        signal/channel to achieve an object that a Tx UE transmits a        synchronization signal and information related to        synchronization to enable an Rx (receiving) UE to match up        time/frequency synchronization with that of the Tx UE.

Although SA and data may use a resource pool separated on a subframe, ifa UE can simultaneously transmit SA and data in a single frame, twotypes of resource pools can be configured in the same subframe.

Moreover, in case that the aforementioned D2D signal content isidentical, a different resource pool is usable according to atransmission/reception attribute of the D2D signal. For example, despitethe same D2D data channel or discovery message, it can be divided into adifferent resource pool again depending on a transmission timingdetermining methodology (whether a D2D signal is transmitted at areception timing of a synchronization reference signal, whether a D2Dsignal is transmitted by applying a constant timing advance at arepletion timing of a synchronization reference signal, etc.), aresource allocation methodology (e.g., whether a transmission resourceof an individual signal is designated to an individual Tx UE by an eNB,or whether an individual Tx UE selects an individual signal transmissionresource from a resource pool by itself), a signal format (e.g., thenumber of symbols occupied in a single subframe by each D2D signal, thenumber of subframes used for transmission of a single D2D signal), asignal strength from an eNB, a transmit power level of a D2D UE and thelike.

For clarity of description, a method for an eNB to directly indicate atransmission resource of a D2D Tx UE in D2D communication is defined asMode 1. And, a method for a UE to directly select a transmissionresource, when a transmission resource region is configured in advanceor an eNB designates a transmission resource region, is defined as Mode2. In case of D2D discovery, a case that an eNB directly indicates aresource is defined as Type 2. And, a case that a UE directly selects atransmission resource from a previously configured resource region or aresource region indicated by an eNB is defined as Type 1.

Moreover, as described above, D2D may be called sidelink, SA may becalled Physical Sidelink Control Channel (PSCCH), D2D synchronizationsignal may be called Sidelink Synchronization Signal (SSS), controlchannel carrying most basic information, which is transmitted togetherwith SSS before D2D communication, may be called Physical SidelinkBroadcast Channel (PSBCH) or Physical D2D Synchronization Channel(PD2DSCH).

Furthermore, a signal for a specific UE to announce that it is locatednearby (here, ID of the specific UE may be included in this signal) orsuch a channel may be called Physical Sidelink Discovery Channel(PSDCH).

According to Rel. 12 on LTE system, only a D2D communication UEtransmits PSBCH together with SSS in D2D, whereby measurement of SSS isperformed using DMRS of PSBCH. An out-coverage UE measures DMRS of PSBCHand then determines whether to become a synchronization source bymeasuring RSRP of this signal and the like.

It is expected that control and data channels coexist in V2Xcommunication. It is assumed that when control and data channels areassociated with each other, multiple vehicles transmit periodicmessages. Assuming that a vehicle is a UE, the UE may know the resourcelocations of currently transmitted messages by decoding the controlchannel or performing energy sensing on the data channel. In addition,the UE may know even the resource locations to be used by othertransmitting UEs.

Based on the above-described technical features, the present disclosuredescribes a method of solving a problem that when a receiving devicelocated at the edge of coverage of a transmitting device (or a receivingdevice that receives a signal broadcast by the transmitting end)transmits ACK/NACK, if the reliability of the ACK/NACK transmission tothe transmitting device is low, the transmitting device fails to receivethe ACK/NACK. Specifically, when a transmitting device transmits asignal within its transmission coverage, a receiving device may receivethe signal. However, if the strength of the received signal is low, thereliability of ACK/NACK transmission may be degraded. To solve such aproblem, the present disclosure proposes the following methods.

In general, additional resources may be allocated to improve thereliability of transmission. However, considering that there is alimited amount of resources, resource allocation needs to be performedefficiently.

To this end, the HARQ ACK/NACK transmission method has been used in LTE.That is, when an eNB transmits data, a receiving UE attempts to decodethe data. If the UE successfully decodes the data, the UE feeds backACK. On the contrary, if the UE fails to decode the data, the UE feedsback NACK to the eNB. When the eNB receives the NACK, the eNB performsretransmission. Thus, the receiving UE may further improve the decodingsuccess probability using the previous transmission and retransmission.Compared to a method of using many resources for reliabilityimprovement, this method is advantageous in that fewer resources areused to achieve the same purpose.

However, as the distance between the transmitting and receiving devicesincreases, the decoding failure probability of the receiving device mayincrease. In addition, when the receiving device transmits NACK toinform the decoding failure, the transmitting device may fail to decodethe NACK due to the long distance. Consequently, the receiving end maybe likely to fail to receive data. In general, the receiving device mayincrease power to overcome such failure. However, in some cases, thereceiving device cannot further increase the power.

Therefore, the present disclosure proposes a method of configuring adifferent ACK/NACK resource size depending on the distance betweentransmitting and receiving devices (or between receiving devices in thecase of broadcast transmission).

For example, the distance between transmitting and receiving devices (orbetween receiving devices in the case of broadcast transmission) may becalculated based on reference signal received power (RSRP) between thetransmitting and receiving devices or information on the locationsthereof. For example, if the RSRP is high, the distance may be assumedto be short. On the contrary, if the RSRP is low, the distance may beassumed to be long.

Therefore, the ACK/NACK resource size may be changed depending on therange of the relative distance value, which depends on the RSRP orlocation information. In this case, the RSRP value may mean the powervalue of a reference signal (RS) transmitted by the transmitting deviceor the received signal strength indication (RSSI) of a signal includingat least one of the transmitted data or the transmitted RS. In addition,mapping between the RSRP value (the relative distance value based on thelocation information or the RSSI value) and the ACK/NACK resource sizevalue may be provided through RRC signaling.

As another example, when a transmitting device does not know the size ofan ACK/NACK resource to be used by a receiving device (or receivingdevices in the case of broadcast transmission), if the sequence of ademodulation reference signal (DMRS) transmitted for ACK/NACKdemodulation is configured differently for each ACK/NACK resource, thetransmitting device may obtain the ACK/NACK resource size by performingblind decoding for the DMRS sequence.

The smallest ACK/NACK resource may be predefined or preconfigured. Usingthe smallest ACK/NACK resource as a unit, an ACK/NACK resource largerthan the smallest ACK/NACK resource may be set to a multiple of thesmallest ACK/NACK resource. Thus, each ACK/NACK resource may be obtainedby combining a plurality of smallest ACK/NACK resources. In this case,each of the smallest ACK/NACK resources may be configured to have adifferent DMRS. This could be simply achieved while different ACK/NACKresources are designed. However, the number of required DMRSs mayincrease as the size of a resource increases.

As a further example, when a transmitting device does not know the sizeof an ACK/NACK resource to be used by a receiving device (or receivingdevices in the case of broadcast transmission), if ACK/NACK istransmitted in the form of a sequence, the ACK/NACK sequence may beconfigured differently for each ACK/NACK resource size. By doing so, thetransmitting device may obtain the resource size by performing blinddecoding for the ACK/NACK sequence.

The length of a sequence transmitted on the smallest ACK/NACK resource,which is predefined or preconfigured, may be used as a unit. That is, asequence transmitted on an ACK/NACK resource larger than the smallestACK/NACK resource may be configured to have a length corresponding to amultiple of the shortest sequence length. Thus, a sequence transmittedon each ACK/NACK resource may be obtained by repeating a plurality ofsequences with the same length as that of the sequence transmitted onthe smallest ACK/NACK resources. This may reduce the complexity of blinddecoding, which is performed by the transmitting device to estimate theACK/NACK resource size.

The present disclosure may be applied only to a receiving device havinglimited power (hereinafter, such a device is referred to as apower-limited receiving device). Specifically, the receiving device maycalculate power required for ACK/NACK transmission and then compare thecalculated power with power that the receiving device can use forreception. If the former is greater than the latter, the presentdisclosure may be applied. For example, in the case of a receivingdevice with no power limitation, the ACK/NACK configuration is notchanged for each resource size in a resource pool configured for thecorresponding device. However, when ACK/NACK resource allocation isperformed using a resource pool configured for a power-limited receivingdevice, the ACK/NACK configuration may be changed for each resource.

According to the present disclosure, whether the configuration accordingto the present disclosure is applied or not may be informed by higherlayer signaling (e.g., RRC signaling) or control information on acontrol channel from a transmitting device. For example, when it isindicated that the present disclosure is not applied, a specificACK/NACK resource may be determined regardless of RSRP (RSSI or arelative distance based on location information) between transmittingand receiving devices.

When the present disclosure is applied, a transmitting device maydirectly inform a receiving device of an ACK/NACK resource sizedepending on, for example, RSRP (RSSI or a relative distance based onlocation information) between the transmitting and receiving devicesusing control information on a control channel. When the transmittingdevice directly informs the receiving device of the ACK/NACK resourcesize, the receiving device may not need to determine the ACK/ANCKresource size.

When the transmitting device directly informs the receiving device ofthe ACK/NACK resource size, the transmitting device may indicate one ofthe predetermined ACK/NACK resource sizes (for example, a list ofACK/NACK resource sizes). In this case, if the number of ACK/NACKresource sizes is different or if a different ACK/NACK resource is used,the transmitting device may inform the receiving device of the type of aphysical format to be used through higher layer signal (or RRCsignaling).

FIG. 12 illustrates a base station (BS) and a user equipment (UE)applicable to an embodiment of the present invention.

If a relay node is included in a wireless communication system, backhaullink communication is performed between the BS and the relay node, andaccess link communication is performed between the relay node and theUE. Therefore, the BS or UE shown in the drawing may be replaced withthe relay node in some cases.

Referring to FIG. 12, a wireless communication system includes a basestation (BS) 110 and a user equipment (UE) 120. The base station 110includes a processor 112, a memory 114 and an RF (radio frequency) unit116. The processor 112 can be configured to implement the proceduresand/or methods proposed in the present invention. The memory 114 isconnected to the processor 112 and stores various kinds of informationrelated to operations of the processor 112. The RF unit 116 is connectedto the processor 112 and transmits and/or receives radio or wirelesssignals. The user equipment 120 includes a processor 122, a memory 124and an RF unit 126. The processor 122 can be configured to implement theprocedures and/or methods proposed in the present invention. The memory124 is connected to the processor 122 and stores various kinds ofinformation related to operations of the processor 122. The RF unit 126is connected to the processor 122 and transmits and/or receives radio orwireless signals. The base station 110 and/or the user equipment 120 canhave a single antenna or multiple antennas.

The above-described embodiments may correspond to combinations ofelements and features of the present invention in prescribed forms. And,it may be able to consider that the respective elements or features maybe selective unless they are explicitly mentioned. Each of the elementsor features may be implemented in a form failing to be combined withother elements or features. Moreover, it may be able to implement anembodiment of the present invention by combining elements and/orfeatures together in part. A sequence of operations explained for eachembodiment of the present invention may be modified. Some configurationsor features of one embodiment may be included in another embodiment orcan be substituted for corresponding configurations or features ofanother embodiment. And, it is apparently understandable that a newembodiment may be configured by combining claims failing to haverelation of explicit citation in the appended claims together or may beincluded as new claims by amendment after filing an application.

In this disclosure, a specific operation explained as performed by abase station can be performed by an upper node of the base station insome cases. In particular, in a network constructed with a plurality ofnetwork nodes including a base station, it is apparent that variousoperations performed for communication with a user equipment can beperformed by a base station or other network nodes except the basestation. In this case, ‘base station’ can be replaced by such aterminology as a fixed station, a Node B, an eNodeB (eNB), an accesspoint and the like.

The embodiments of the present invention may be implemented usingvarious means. For instance, the embodiments of the present inventionmay be implemented using hardware, firmware, software and/or anycombinations thereof. In case of the implementation by hardware, oneembodiment of the present invention may be implemented by at least oneof ASICs (application specific integrated circuits), DSPs (digitalsignal processors), DSPDs (digital signal processing devices), PLDs(programmable logic devices), FPGAs (field programmable gate arrays),processor, controller, microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, one embodiment ofthe present invention may be implemented by modules, procedures, and/orfunctions for performing the above-explained functions or operations.Software code may be stored in a memory unit and may be then driven by aprocessor.

The memory unit may be provided within or outside the processor toexchange data with the processor through the various means known to thepublic.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

INDUSTRIAL APPLICABILITY

The method of allocating an ACK/NACK resource in a wirelesscommunication system and apparatus therefor can be applied to variouswireless communication systems.

1. A method of feeding back acknowledgement/negative-acknowledgement(ACK/NACK) by a receiving device in a wireless communication system, themethod comprising: receiving data from a transmitting device; andfeeding back ACK/NACK for the data to the transmitting device, wherein aresource size of the ACK/NACK is determined based on a distance betweenthe transmitting device and the receiving device.
 2. The method of claim1, wherein the resource size of the ACK/NACK is determined as a resourcesize associated with a specific range corresponding to a distance valuedepending on reference signal received power (RSRP) or locationinformation based on a predetermined range for the resource size of theACK/NACK.
 3. The method of claim 2, wherein information on thepredetermined range and the resource size of the ACK/NACK mapped to thepredetermined range are indicated through radio resource control (RRC)signaling.
 4. The method of claim 1, further comprising transmitting ademodulation reference signal (DMRS) associated with the ACK/NACK to thetransmitting device, wherein a DMRS sequence is determined based on theresource size of the ACK/NACK.
 5. The method of claim 1, wherein anACK/NACK sequence is determined based on the resource size of theACK/NACK.
 6. The method of claim 1, wherein only when the ACK/NACKresource is selected from a resource pool configured for a power-limitedreceiving device, the resource size of the ACK/NACK is determined basedon the distance between the transmitting device and the receivingdevice.
 7. The method of claim 1, wherein only when it is indicatedthrough higher layer signal or a control channel that the resource sizeof the ACK/NACK is determined based on the distance between thetransmitting device and the receiving device, the resource size of theACK/NACK is determined based on the distance between the transmittingdevice and the receiving device.
 8. The method of claim 1, wherein theresource size of ACK/NACK is indicated by the transmitting device basedon the distance between the transmitting device and the receivingdevice.
 9. A method of receivingacknowledgement/negative-acknowledgement (ACK/NACK) by a transmittingdevice in a wireless communication system, the method comprising:transmitting data to a receiving device; and receiving ACK/NACK feedbackfor the data from the receiving device, wherein a resource size of anACK/NACK is determined based on a distance between the transmittingdevice and the receiving device.
 10. A receiving device for feeding backacknowledgement/negative-acknowledgement (ACK/NACK) in a wirelesscommunication system, the receiving device comprising: a radio frequencyunit; and a processor, wherein the processor is configured to receivedata from a transmitting device and feed back ACK/NACK for the data tothe transmitting device, and wherein a resource size of an ACK/NACK isdetermined based on a distance between the transmitting device and thereceiving device.
 11. The receiving device according to claim 10,wherein the receiving device is capable of communicating with at leastone of another transmitting device, a transmitting device related to anautonomous driving vehicle, a base station or a network.